If by "too many times" you mean less than, say, 100, you shouldn't have any problems.

When purchasing a used computer, your best best is to do an erase and install of the OS, during which time you can select the installation options (such as languages, etc.) that you need. Most likely this will result in less disk space being used vs. more, depending upon how the system was originally installed.

Deleting system files manually is probably something you shouldn't be doing if you're not familiar with how everything works together.

Anything that requires more disk access will lead to more wear and tear. Secure erasing, which generally involved overwriting "blank" areas of the disk with a series of information, will always be more effort, and hence more wear and tear, than simply removing a directory entry and leaving the data on the drive.

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